The Vermont Hazardous Materials Response Team recently found itself responding to an unusual call at a road paving site.
The VT Digger reported that one of New England’s largest paving companies had a piece of paving equipment malfunction, dumping 2,200 gallons of tar-like liquid on a project site in Springfield, Vt.
“I’ve been on the state hazmat team for a number of years myself and on the (Springfield) department for over 17 years,” Springfield Fire Department Deputy Chief Paul Stagner told VT Digger. “This is the first time I’ve ever seen something like this happen with this piece of equipment.”
The hazmat team had to keep the material from reaching a nearby waterway.
“Quite a bit of material did leak, but it was all contained relatively quickly onto the road and into a dirt area that was dug up,” Stagner said.
The waterway contamination was quickly mitigated by using sand piles to create dams, Stagner said. The contaminant was a tar-like substance that doesn’t have its own hazmat ID number. It does not harden in the way that concrete would, he said.
Hazmat issues with asphalt concrete are most likely to occur at the plant, where binding agents are blended with the aggregate — broken rock — material. However, as Vermont’s hazmat team saw, site work incidents can and do happen.
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There are several mixes and methods for paving with asphalt, but hot-mix asphalt is most often used on high-traffic roadways. As the name implies, the mixture is stored and applied hot — about 300 degrees Fahrenheit.
Lehigh-Hanson, one of the world’s top mining and construction materials producers, issued a nine-page safety data sheet on hot-mix asphalt.
Mostly due to the silica content, long-term, repeated exposure to hot-mix asphalt can cause respiratory damage and cancer. When heated, the mixture puts off hydrogen sulfide gas. And, of course, there is the immediate threat of being burned by the hot substance.
For accidental releases, the data sheet has this recommendation. “If hot product is spilled, evacuate unnecessary personnel, remove all heat and ignition sources and provide explosion proof ventilation. Use water spray to reduce vapors. Wear appropriate protective equipment and clothing during clean-up of materials that contain dust.”
The sheet instructs firefighters to wear full PPE and SCBA and to be cautious not to let it come in contact with powerful oxidizing agents, as that can cause fire or explosion. And again, the hotter it gets, the more hydrogen sulfide it will release.
Thermal decomposition may release carbon monoxide, carbon dioxide, hydrogen sulfide, nitrogen dioxide, ozone and other organic and inorganic compounds. Silica dissolves in hydrofluoric acid producing a corrosive gas-silicon tetrafluoride.
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